US4420800A - Reflector lamp with shaped reflector and lens - Google Patents

Abstract

A reflector lamp with a shaped reflector and lens. The reflector is generally parabolic, to reflect light frontwardly. Some of the direct light from the light source is not reflected, and diverges in a beam pattern that would be wasted; the lens refracts this divergent light in a more frontwardly and useful direction. For a floodlight, the lens converges the reflected light rays into a crossover pattern to provide a flood beam pattern.

Description

REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending application Ser. No. 218,932, filed Dec. 22, 1980 and now abandoned.

U.S. Patent Application Ser. No. 352,741, filed Feb. 26, 1982, of Reiling, Putz, and Van Horn, entitled "Reflector Lamp" assigned to the same assignee of the present invention and which is a continuation-in-part of U.S. Patent Application Ser. No. 165,610, filed July 3, 1980, now abandoned.

BACKGROUND OF THE INVENTION

The invention is in the field of reflector lamps, such as floodlights and spotlights, having reflectors and lenses. In such lamps, the light source is deeply recessed in a concave reflector which reflects frontwardly in a desired beam pattern substantially more than half of the total light output of the lamp.

The above-referenced patent applications Ser. Nos. 165,610 and 352,741 disclose a reflector lamp having a concave reflector comprising parabolical and spherical sections, for projecting a pattern of parallel light rays in a frontward direction. In the use of a concave reflector lamp, there is an undesirably wasted amount of light which emanates from the light source and is not reflected but radiates in a divergent cone pattern through the front of the reflector.

SUMMARY OF THE INVENTION

Objects of the invention are to provide a reflector lamp, combined with a lens, having improved optical efficiency which permits a design having lower power consumption, and to achieve this with a reasonably compact lamp.

The invention comprises, briefly and in a preferred embodiment, a reflector lamp having a concave reflector, which may have one or more parabolic sections, for reflecting light frontwardly from a finite light source located substantially at the focal point. The light source is deeply recessed in the reflector so as to be at least three times as far from the front opening of the reflector as from the reflector vertex so that substantially more than half of the total light from the light source is reflected by the reflector. A lens is positioned over the front of the reflector and is contoured at least near the outer edge thereof to refract frontwardly at least some of the unreflected divergent light emanating directly from the light source. For a floodlight, substantially the entire lens is contoured to refract and converge light rays including the reflected light rays, so that the reflected light rays converge into a crossover pattern to provide a flood beam pattern.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a front view of a reflector lamp in accordance with a preferred embodiment of the invention.

FIG. 2 is a cross section side view taken on theline 2--2 of FIG. 1.

FIG. 3 is a side view of the lamp and a floodlight beam pattern.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the invention, as shown in the drawing, comprises a reflector lamp having aconcave reflector 11 shaped to have afront reflector section 12 which has a substantially parabolic contour with respect to a focal point 13, anintermediate reflector section 14 which has a substantially spherical contour with respect to the focal point 13, and arear reflector section 15 which has a substantially parabolic contour with respect to the focal point 13. The cross-section of thereflector 11 perpendicular to its principal optical axis is circular, as shown in FIG. 1. Thus, each of the three reflector sections is defined by a surface of revolution of a parabolic or a circular curve. A finite light source, that is, a light source that is neither infinite nor infinitesimal in size such as afilament 16 is centered at the focal point 13 and generally is either perpendicular or parallel to the lamp axis. Preferably thelight source 16 is located in or near the plane 17 of mutual truncation at the joinder of thefront section 12 andintermediate section 14, as shown in the drawing.

To achieve the maximum practical optical efficiency, reflector lamps are designed to have thereflector 11 as deep as is feasible, to provide a large primary reflectingsurface area 12 for reflecting substantially more than half of the total light into the desired beam pattern. Additionally, substantially less than half of the total amount of light emanates directly and unreflected from thelight source 16 through the front of the reflector in a divergent pattern whereby some of the light is wasted because it falls outside of the desired beam pattern. Thus, thelight source 16 is deeply recessed in the reflector and is typically at least three times the distance from the front plane orrim 31 of the reflector than from the vertex, or virtual vertex 12' in the embodiment shown, of the primary reflectingsurface 12. The desired long depth of the reflector is limited by practical considerations such as not wanting unduly great size, weight, bulk, and cost of the reflector. Alternative light sources can be employed in place of thefilament 16, such as a halogen regenerative-cycle incandescent lamp or an arc discharge lamp. Ashaped lens 20 is placed or sealed over the front opening of thereflector 11, primarily to modify the light pattern, as will be described below. Additionally the lens serves to protect the reflecting surface and thereby keeps the reflector surface clean. Furthermore a cover or lens is required if the light souce is abare filament 16. Thereflector 11 can be made of molded glass, its inner surface being coated with aluminum or silver to provide a reflective surface. Preferably thefilament 16 is made of tungsten and is mounted on a pair of lead-inwires 18, 19 of suitable material such as nickel.

Although in the preferred embodiment the focal points of the parabolic and spherical sections are substantially confocal, the focal point of the spherical intermediate section need not be located at substantially the same spatial position as the focal points of the parabolic sections while remaining within the scope of this invention. More specifically, the focal point of the spherical section can be located between the common focal points of the parabolic sections and a point spaced therefrom located not greater than ten times the maximum light source dimension which is perpendicular to the light source major axis. In such an embodiment, the finite light source would be positioned substantially at the common focal points of the parabolic sections.

Similarly, although in the preferred embodiment the finite light source is positioned substantially at the confocal points of the parabolic and spherical sections, the finite light source can be located elsewhere while remaining within the scope of this invention. That is, the light source can be positioned either perpendicular or parallel to the lamp axis and between the confocal points of the parabolic and spherical sections and a point spaced therefrom, located not greater than ten times the maximum light source dimension which is perpendicular to the light source major axis.

Light rays which emanate from thelight source 16 at the focal point 13 and which strike the parabolicfront reflector section 12, will be reflected in a generally frontward direction, as indicated by thelight ray paths 21. Similarly,light rays 22 emanating from thefilament 16 and which strike the parabolicrear reflector section 15, will be reflected generally frontwardly.

As is disclosed and claimed in the above-referenced patent applications, the sphericalintermediate section 14 is dimensioned with respect to the parabolicfront reflector section 12 so that substantially all of the light emanating from thelight source 16, other than at focal point 13 and which strikes the sphericalintermediate section 14, will be reflected thereby in a direction so as to strike theparabolic front section 12 and be re-reflected thereby in a generally frontward direction. For example, alight ray 26 emanating from thelight source 16, strikes the intermediatespherical section 14 and is reflected onto the parabolicfront reflector section 12 and is directed frontwardly as shown in FIG. 2.

It is to be noted, however, that light rays reflected by the intermediatespherical section 14 and which emanate from thelight source 16 at focal point 13 will not be reflected in a direction so as to strike theparabolic front section 12. More specifically, and as well known in the art, a ray of light emitted from a light source at a specific wavelength and reflected back onto the light source, at that same wavelength, will either be absorbed and/or re-reflected but will never pass through the light source. Thus, any light rays such as light ray 27, emitted from that portion of thelight source 16, located at the focal point 13, striking the intermediatespherical section 14 will be reflected back along the original light ray path, due to the optical geometry thereof, and intercept thelight source 16 at focal point 13. Assuming that the light ray 27 maintains the same wavelength throughout its path of travel, then upon intercepting thelight source 16 at focal point 13, light ray 27 will be absorbed and/or re-reflected thereby. Light ray 27, will never pass throughlight source 16. Therefore any light rays emitted from thelight source 16, at focal point 13, and which strike the intermediatespherical section 14 and maintain the same wavelength throughout their path of travel, cannot contribute to the total light leaving thelamp 11. In more general terms, and as is well known in the art, any portion of the light source whose reflected image coincides with itself or any other portion of the light source will provide no useful light output inasmuch as the reflected image cannot travel through the actual light source.

A preferred method of designing the reflector, is to first design thefront section 12 and then design the contour of thespherical section 14. Next, a line is drawn from therim 31, and through the focal point 13, to the contour line of theintermediate section 14; this point of intersection establishes the joinder plane 28 at the rear of thesection 14 where it joins therear section 15.

In scientific optical terminology, the breadth of the parabolic reflector curve at the focal point 13 is the latus rectum and is represented in the drawing by the line 17 in FIG. 2, and the vertex is the point on the rear surface directly behind the focal point 13. The vertex of the frontparabolic section 12 is the point thereon that would be directly behind the focal point 13 if the parabolic curvature were to be continued behind the focal point 13. Thus the focal point 13 is relatively close to the vertex of the frontparabolic curve 12 and is substantially farther from the vertex of the rearparabolic curve 15. The diameter of the sphericalintermediate section 14 is essentially equal to the length of the latus rectum 17 of the frontparabolic curve 12.

The space defined and surrounded by the sphericalintermediate section 14 provides a recess for accommodating thelight source 16, and spaces the reflecting surface at the back part of the reflector sufficiently far from thefilament 16 to minimize blackening thereof by evaporated filament material, and accomplishes this while retaining an optical efficiency substantially as good as if the entire reflector had a single parabolic curvature.

Some of the light emanating from thesource 16 is not reflected by thereflector 11, and emerges from thesource 16 in a diverging cone-shaped beam, illustrated by the cone edge pairs oflight rays 33. Another illustrative pair of diverginglight rays 34 within the aforesaid cone-shaped beam, are also shown. This cone-shaped beam, including the cone edge-definingrays 33 and all other rays such asrays 34 contained therein would, but for thelens 20, emerge through the front of thereflector 11 in straight continuation rays 33', 34'. All of the light rays of the cone-shaped beam, except for those on the optical axis, are divergent and inconsistent with the desired frontward substantially parallel ray pattern provided by thereflector 11, and (but for the lens 20) will fall outside the desired beam pattern and will be wasted light in most applications. The closer the cone rays are to theedge defining rays 33, the more divergent they will be, these edge rays 33 being the most divergent and other cone rays such asrays 34 which are slightly within the cone edge rays 33 being only slightly less divergent.

The light rays 21, 32, 33, and 34 are shown as pairs thereof symmetrically arranged about the optical axis of thereflector 11, to better illustrate the light distribution patterns in the cross-sectional view of FIG. 2 and to facilitate illustration in FIG. 3 of a projected floodlight beam pattern.

In accordance with the present invention, thelens 20 is contoured, at least near its outer rim, to refract in a more frontwardly direction at least some of the divergent "stray" light rays from the light source, and the lens may be further contoured to provide a floodlight beam pattern. The preferred contouring of the lens is in the form ofconcentric prisms 36, preferably on its inner surface, of the Fresnel lens type.

In FIG. 2, the dashed-linelight ray representations 21, 22, 26, 32, 33, etc. represent light rays from thesource 16, both reflected and nonreflected within thereflector 11, and the dashed-line representations indicated by primed numbers 21', 22', 26', 32', 33' etc. of these light rays in front of the light unit indicate what the ray patterns and directions would be without the presence of thelens 20. The solid-line representations, indicated by double-primednumbers 21", 22", 26", 32", 33" etc. of these light rays in front of thelens 20 indicate their patterns and directions as modified by the functioning of the lens in accordance with the invention. Furthermore, as illustrated in FIG. 2, although light ray 26' is not strictly parallel to reflected light rays 21' and 32', all of which are reflected by the frontparabolic section 12, the angles between light ray 26' and light rays 21' and 32' are sufficiently small such that 26' is substantially parallel to light rays 21' and 32' and thus conforms to the desired frontward substantially parallel ray pattern to be provided by thereflector 11.

In accordance with the first-mentioned embodiment of the invention, theconcentric prisms 36 are provided on the inner surface of thelens 20 and only near the outer periphery thereof, for example in an outer region of the lens so as to intercept all of the divergent light rays between and including therays 33 and 34. Theseprisms 36 are shaped to be optically convergent, so as to refract the divergent light rays 33, 34 and the divergent rays therebetween, in a more frontwardly direction as indicated by the solid-line rays 33" and 34", and thus more nearly into the desired useful overall beam pattern. At the same time, the reflected and frontwardly directed light rays including therays 21, 32 will be converged inwardly by the lens prisms, as indicated by the solid-line rays 21" and 32", and will cross over at a region 38 (FIG. 3) in front of thelens 20 and thereafter be divergent and directed somewhat out of the desired beam pattern. For purposes of clarity, rays 22 and 26 have not been shown. It is to be understood, however, thatrays 22 and 26 similar torays 21 and 32, would converge inwardly due to the lens prisms and cross over other converging rays such as 21 and 32 at regions similar to region 38. Thus the lens prisms serve two functions, namely, to adjust the direction of the unreflected diverging light rays, that is, the "spill" light, such asrays 33 and 34, in a more frontwardly direction and to direct the substantially parallel light rays such as 21 and 32 in a more inwardly direction. In accomplishing these functions the lens typically is thinnest near the edge thereof.

A compromise can be found in the lens design and its degree of optical convergence, so that more useful light is gained in the desired overall beam pattern by the frontward refraction of the otherwise divergent rays 32', 33' than may be lost due to the convergent refraction of the otherwise substantially parallel rays 21', 22', 26', and 32'. This increases the useful light output and/or permits the use of alower wattage filament 16 thus conserving electrical energy. In this embodiment of providing alens 20 withconcentric prisms 36 only near the periphery of the lens, the reflected and nonreflected light rays fromfilament 16 which pass through the lens central region, such as defined by a circumference bounded by the light rays 21, are substantially unaffected by the lens.

In another embodiment of the invention, a floodlamp having improved electrical and optical efficiency is achieved by providing the light-reflectingconcentric prisms 36 over substantially the entire inner surface of thelens 20, as shown in FIG. 2. These prisms need not be provided at the reflector'scenter area 41 where they would be relatively ineffective. Referring again to FIG. 3, in accordance with the floodlight of the invention, thelens 20 refracts the nonreflected divergent light rays in a more frontwardly divergent pattern, exemplified by the light rays 33" and 34", which is in the desired divergent floodlight beam pattern. Also, thelens 20 refracts the reflected parallel light beams in a convergent manner to produce a crossover pattern of rays which thereafter are divergent in the desired floodlight pattern. For example, the above-describedlight rays 21" and 32" crossover at region 38 in front of thelens 20 and thereafter diverge generally in the desired floodlight beam pattern. For more completeness, FIG. 3 shows an additional pair of projected light rays 42" and 43" which have been reflected by thereflector 11 toward thelens 20 at an intermediate diameter region 44 thereof and refracted by the lens to converge and crossover at a region 46 in front of the lens and thereafter diverge generally in the desired beam pattern. Unreflected light rays passing through the lens at its intermediate diameter region 44 will be refracted and projected approximately frontwardly, thus contributing to the overall flood beam illumination. In lamps built according to the invention, the crossover regions 38, 46 lay in the range of about 5 to 20 inches in front of thelens 20.

Thus in the two embodiments described heretofore the lens design provides for a maximum beam candlepower, that is, beam intensity, along the lamp axis. Additionally the lens provides for half of the maximum beam candlepower at approximately 15.5° or 7° from the lamp axis for a floodlamp or spotlamp, respectively.

A unique feature of the invention is the divergent projection of somelight rays 33" and 34" and the convergent projection of otherlight rays 21', 32", 42", and 43" which light rays cross over and become divergent in a manner compatible with thedivergent rays 33" and 34" to provide a desired floodlight beam pattern. Theconcentric prisms 36 need not have identical refraction angles; the refraction angles of some or all of the various prisms can be different from one another to tailor the light distribution for uniform intensity or other desired characteristics is the projected light beam. By thus providing thelens 20, in cooperation with thereflector 11, most of the projected light rays are in the desired beam pattern and relatively little light is wasted, thus improving efficiency and conserving electrical energy.

While preferred embodiments of the invention have been shown and described, various other embodiments and modifications thereof will become apparent to persons skilled in the art, and will fall within the scope of the invention as defined in the following claims.

Claims (18)

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A reflector lamp comprising a finite light source positioned substantially at the focal point of a reflector, said reflector having a substantially parabolic front section as a primary reflecting surface, a substantially spherical intermediate section, and a substantially parabolic rear section, each of said sections having substantially the same common focal point, said light source located at least three times as far from the front opening of said reflector as from the vertex of said primary reflective surface so that substantially more than half of the total light is reflected by the reflector, and a lens positioned over the front of said reflector and contoured at least near the outer edge thereof to refract in a more frontwardly direction at least some of the unreflected divergent light from said light source.

2. A reflector lamp as claimed in claim 1 wherein said lens contour comprises concentric prisms.

3. A reflector lamp as claimed in claim 2 wherein said concentric prisms are on the inner surface of said lens.

4. A reflector lamp as claimed in claim 1 wherein said reflector is dimensioned so that substantially all light rays from said light source which are reflected by said spherical intermediate section are re-reflected by said parabolic front section.

5. A reflector lamp as claimed in claim 1 wherein substantially an entire surface of said lens is contoured to refract light more inwardly, whereby light reflected by said reflector is converged into a crossover pattern and thereafter diverges to provide a floodlight pattern in cooperation with said refracted unreflected light.

6. A reflector lamp as claimed in claim 5 wherein said lens contour comprises concentric prisms.

7. A reflector lamp as claimed in claim 6 wherein said concentric prisms are on the inner surface of said lens.

8. A reflector lamp as claimed in claim 5 wherein said reflector is dimensioned so that substantially all light rays from said light source which are reflected by said spherical intermediate section are re-reflected by said parabolic front section.

9. A reflector lamp comprising a finite light source positioned substantially at the focal point of a reflector, said reflector having a substantially parabolic front section as said primary reflective surface, a substantially spherical intermediate section, and a substantially parabolic rear section, each of said sections having substantially the same common focal point, said light source located at least three times as far from the front opening of the reflector as from the vertex of said primary reflective surface so that substantially more than half of the total light from said light source is reflected frontwardly by said reflector, and substantially less than half of the total light emerges at the reflector front opening unreflected and in the form of a divergent cone of light, and a lens positioned over the front of said reflector and contoured to refract substantially all of said light in a more inwardly direction whereby said unreflected light remains divergent and said reflected light is converged into a crossover pattern and thereafter diverges to provide a floodlight pattern in cooperation with said refracted, unreflected light.

10. A reflector lamp as claimed in claim 9 wherein said lens causes the divergent angles of said reflected light after crossover to be approximately the same as the divergent angles of said unreflected light in the projected light pattern.

11. A reflector lamp as claimed in claim 9 wherein said reflector is dimensioned so that substantially all light rays from said light source which are reflected by said spherical intermediate section are re-reflected by said parabolic front section.

12. A reflector lamp as claimed in claim 9 wherein said lens contour comprises concentric prisms.

13. A reflector lamp as claimed in claim 12 wherein said concentric prisms are on the inner surface of said lens.

14. A reflector lamp as claimed in claim 1 or 9 wherein said finite light source lies substantially in a plane perpendicular to the lamp axis and intersects said focal point.

15. A reflector lamp as claimed in claim 1 or 9, wherein said finite light source lies substantially in a plane perpendicular to the lamp axis; said plane located at a distance from said focal point which is not greater than ten times the maximum light source dimension which is perpendicular to the light source major axis.

16. A reflector lamp as claimed in claim 1 or 9 wherein said finite light source lies substantially in a plane which includes the lamp axis and said focal point.

17. A reflector lamp as claimed in claim 1 or 9 wherein said finite light source lies substantially in a plane parallel to the lamp axis; said plane positioned at a distance from said focal point which is not greater than ten times the maximum light source dimension which is perpendicular to the light source major axis.

18. A reflector lamp as claimed in claim 4, 8 or 11 wherein said focal point of said spherical section is located between said common focal points of said parabolic sections and a point spaced therefrom located not greater than ten times the maximum light source dimension which is perpendicular to the light source major axis.

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